Medical devices can perform tasks including monitoring, detecting, or sensing physiological information, diagnosing a physiological condition or a disease, treating or providing a therapy for a physiological condition or disease, or restoring or otherwise altering physiologic function. For example, such medical devices include implantable devices or externally-worn ambulatory devices. An example of an implantable medical device can include a cardiac function management device, such as a pacemaker, a cardiac resynchronization therapy device, a cardioverter or defibrillator, or other device. Other medical devices can include a neurological stimulator, a neuromuscular stimulator, a drug delivery system, or one or more other devices.
Generally, a medical device can include a wireless communication circuit (e.g., a telemetry circuit) and an antenna coupled to the wireless communication circuit, to provide wireless communication between the medical device and another assembly, such as to send information (e.g., physiological or other information) from the medical device to another assembly, or to receive information (e.g., programming instructions, operational parameters, or other information) from another assembly. Mutual inductive coupling can be used to provide short-range communication between an implantable medical device implanted in a body and an external assembly, or between a medical device outside of the body and an external assembly.
Communication via mutual inductive coupling largely relies on low frequency near-field coupling, where the field distribution is highly dependent upon the distance from, and orientation of, the antenna. Such mutual inductive coupling can grossly limit the range of wireless communication between the implantable medical device and the external assembly, generally to a range of a few centimeters.